This invention relates to a black matrix color cathode-ray tube and, more particularly, to a high-definition black matrix color display vacuum tube.
In the manner which is known in the art and will later be described in greater detail, a black matrix color cathode-ray tube comprises a face panel enclosing a vacuum space, red or magenta, green, and blue or cyan luminescent patterns, namely, luminescent patterns of three additive primaries, on the face panel inside the vacuum space, and an electron gun in the vacuum space opposite to the face panel. The electron gun directs an exciting electron beam selectively onto the red, the green, and the blue luminescent patterns to make the red, the green, and the blue luminescent patterns emit red, green, and blue rays through the face panel. During manufacture, a black or light absorbing film of, for example, graphite is formed on an inside surface of the face panel and its adjacency and a photoresist film is formed on the black film. Using a shadow mask, an optical beam is directed onto the photoresist film to eventually form openings where the red, the green, and the blue luminescent patterns are subsequently deposited. In this manner, a black matrix film is formed. It is possible to use a photosensitive luminescent material on subsequently manufacturing each set of the red, the green, and the blue luminescent patterns.
In Japanese Patent Prepublication (A) No. 164,143 of 1988, an improved black matrix color cathode-ray tube is disclosed. It is inevitable during an opening forming process (which takes from 90 to 120 seconds for providing the openings for the red, the green, and the blue pattern sets) that the photoresist film has a gradually reduced temperature, such as from 42.degree. C. to 35.degree. C. in an ambient temperature of 25.degree. C . It will be assumed that the optical beam is incident onto the photoresist film with an exposure spot given an area kept constant and that first through third sets of openings are successively formed for one and other of the red, the green, and the blue pattern sets.
When PAA (polyacrylamide) is used as a photoresist material, each opening of the first set has the smallest area with each opening of the second set and of the third set given successively wider areas. When PVA (poly(vinyl alcohol)) or ADC (ammonium dichromate) is used as the photoresist material, each opening of the first set has the widest area with each opening of the second and the third sets given successively smaller areas. On the other hand, it is said in the Japanese patent prepublication that a uniformity in a display of achromatic or hue-less white color is achieved when the red luminescent pattern is smaller in area than the blue luminescent pattern and moreover when the blue luminescent pattern is smaller in area than the green luminescent pattern.
However, it should be taken into account that the exciting electron beam may not necessarily hit at only one of the red, the green, and the blue luminescent patterns that is intended. Instead, the electron beam may concurrently hit at a part of an adjacent luminescent pattern. This phenomenon frequently occurs resulting in an undesirable additive color mixture particularly when the color cathode-ray tube is a high-definition one or when the cathode-ray tube is a wide aperture one having a short tube length as used for a color display device in terminal equipment.
It will later be quantitatively described that the undesirable additive color mixture of each of basic or pure green and blue colors to a basic red color deteriorates saturation or chroma of the basic red color. In addition, it should be noted as will later be exemplified that such a color mixture between the basic red and green colors results in an appreciable amount of change in chromaticity of the color to give rise to a consequent reduction of tolerance in the saturation of the color as a result of luminous efficacy of the human eye. Although improvement of the uniformity in the achromatic white color is feasible by a change in the process of fluorescent pattern deposition, it is impossible to cope with the deterioration in the saturation of a basic color.